Field Of The Invention
This invention relates to a dosimeter and in particular to a dosimeter designed for individual use that has a constant air stream flowing through the dosimeter.
Dosimeters are known and have been used by individuals in an effort to determine the level of exposure of an individual to foreign substances in air, for example, to vapors or fumes, dust particles and the like. The dosimeter is worn by the individual and air is pumped through a filter which traps foreign substances in the air. At the end of an individual's exposure period, the filter is removed and analyzed for any foreign substances. The problem has been with these dosimeters that the air flow rate through the dosimeter has not been accurately controlled. For example, if the filter was partially blocked so that intake of air was momentarily stopped or reduced for a period of time, it was not possible to adjust and increase the flow rate of air to compensate for the stoppage or reduction of air passing through the filter of the dosimeter. Any reduction in the air flow rate reduces the amount of foreign substances collected by the filter thereby giving an inaccurate level of exposure of the individual.
The aforementioned problem has been substantially solved with the dosimeter described in Baker et al. U.S. Pat. No. 4,063,824 issued Dec. 20, 1977. However, dosimeters requiring an air flow rate of about 1-3 liters per minute present special problems and require additional control of the air being pumped through the dosimeter to provide a uniform smooth air flow rate.